Xenon lamp

ABSTRACT

A high pressure xenon discharge lamp whose envelope has tubular portions extending from an enlarged central portion, the ends of the tubular portions being sealed by internal metal shells closed at their inner ends, in which the electrode rods are embedded in glass stems whose outer ends are attached to the tubular portions of the envelope and whose inner ends are spaced from the tubular portions, allowing the tubular portions to be of sufficient diameter for the lamp to be supported from the ends of the tubular portions while avoiding excessive thickening of the walls of the tubular portions.

i United States Patent 1151 3,660,711

Stanyon et a]. 1 May 2, 1972 54] XENON LAMP [56] m References Cited [72]Inventors: Horace Edward Stanyon; Kenneth Buckley UNITED STATES PATENTSRebinson; Eric John George of 2,965,790 l2/l960 lttig et al .313/217London, England 2,781,470 2/1957 Bellott [73] Assignee: Thorn LightingLimited, London, England Pnmary Examiner-Roy Lake [22] Filed: Mar. 17,1970 Assistant Examiner-Darwin R. Hostetter Attorney-Laurence Burns [21]Appl. No.: 20,173

57 ABSTRACT Foreign Application Priority Data A high pressure xenondischarge lamp whose envelope has tubular portions extending from anenlarged central portion, the Mar. 19, 1969 Great Brltam ..l4,525/69ends of the tubular portions being Sealed y internal metal shells closedat their inner ends, in which the electrode rods 52 US. Cl ..313/220,313/184, 313/217, are embedded in glass stems whose outer ends areattached to 313/244 the tubular portions of the envelope and whose innerends are [51] lnt.Cl. ..H01j61/36 spaced from the tubular portions,allowing the tubular por- [58] Field of Search ..313/184, 217, 220, 331tions to be of sufiicient diameter for the lamp to be supported from theends of the tubular portions while avoiding excessive thickening of thewalls of the tubular portions.

3 Claims, 2 Drawing Figures Patented May 2, 1972 HORACE EDWARD STANYONKENNETH BUCKLEY ROBINSON ERIC JOHN GEORGE BEESON INVENTORS BY; g

ATTORNEY XENON LAMP The present invention relates to high-pressure xenondischarge lamps such as compact source or short are xenon lamps.

These lamps are generally designed to operate with an internal gaspressure of many atmospheres. The lamp envelope, which is generally madeof fused silica, and the seals through which current-carrying leadsenter the lamp are designed to contain this high pressure and to avoidthermal stresses in the lamp body which could result in lamp failure bybursting. Since the lamps are normally used in static equipmentmechanical strength is a secondary consideration. However when theexisting lamps are subject to vibration or shock they tend to fail bycracking at certain weak points in the envelope.

One particular point of weakness is where the envelope surrounds theelectrode structure, which is of rod formation. While the centralportion of the envelope is bulbous, and commonly spherical, the portionssurrounding the electrode structures are tubular and are reduced indiameter to engage and support the electrode structures. Since the lampis normally supported at the outer ends of the tubular portions of theenvelope these reduced diameter sections are points of weakness. Thediameter cannot be increased by increasing the wall thickness since thisresults in increased risk of thermal stresses which will also weaken thelamp.

In accordance with the present invention there is provided ahigh-pressure xenon discharge lamp having electrode structures of rodformation supported within tubular portions of the envelope extendingfrom a central enlarged portion of the envelope, in which part of thelength of each of the electrode structures is embedded in a stem whoseouter end is supported within the tubular portion of the envelope andwhose inner end is spaced from the tubular portion of the envelope.

Where the outer ends of the tubular portions of the envelope are closedby tubular metal shells sealed within the tubular portions the outer endof the stem is supported by the closed inner end of the metal shell andby the wall of the tubular portion. The inner ends of the stems can belocated with respect to the tubular portions by projections.

To increase the mechanical strength at the ends of the envelope fromwhich the lamp is supported a metal cap is fitted on the end of theenvelope and is secured to a metal rod which extends into the shellclosing the end of the envelope and is packed tightly withheat-resisting material. A recess at the outer end of the rod serves forthe mechanical support of the rod and electrical connection is made byway of the cap and molybdenum foils sealed between the envelope and thetubular shell.

The invention will now be described in more detail with the aid of anexample illustrated in the accompanying drawings, in which:

FIG. 1 is a longitudinal section of a xenon arc lamp in accordance withthe invention, and

FIG. 2 is a section on an enlarged scale of one limb of the lampenvelope, showing the end cap construction.

Referring first to FIG. 1, the lamp envelope has a central portion whichin this instance is of spherical shape. It may alternatively beelongated or of isothermal shape and it may have an auxiliary startingprobe fitted. The envelope has a uniform wall thickness of about 2 to 4mm. which enables it to operate at temperatures of 800 C. and higherwithout any risk of bursting. The ends of the envelope are formed bytubular portions 11 and 12 of uniform diameter which are closed at theirouter ends by tubular metal shells l3 and 14, respectively, sealedwithin the tubular portions of the envelope. The electrodes of the lamphave rods 15 and 16 which serve as supports and as electricalconductors. The rods 15 and 16 are located within the tubular portions11 and 12, respectively, and in a conventional lamp would be in directcontact with the inner surface of a thickened portion of the wall of thetubular portion, the outside diameter of the tubular portion beingreduced to avoid undue thickening and the consequent risk of thermalstresses.

In the construction shown, however, the rods 15 and 16 are embedded inrespective stems l7 and 18 which are fixed at their outer ends betweenthe closed inner end of the tubular metal shell 13 or 14 and the innerwall of the tubular portion 11 or 12. Projections 19 on the inner endsof the stems l7 and 18 engage the inner walls of the tubular portions 11and 12 and thus locate the stems. In this way the tubular portions 11and 12 of the envelope can have a uniform diameter of suffcientmagnitude to achieve the required strength while the electrode rods arestill firmly supported and the risk of thermal stresses is minimized.The thickened portion of the stem is at its outer end where thetemperature is lower. The diameter of the tubular portions 11 and 12 canbe up to half that of the bulb and with a wall thickness equal to orcomparable with that of the bulb they can easily be annealed toeliminate thermal stresses.

The ends of the envelope are fitted with metal caps 20 having ferrules21 formed with conical recesses 22 by means of which the lamp can belocated and supported. As shown in FIG. 2 the ferrule 21 at each end ofthe lamp is screwed onto the end of a metal rod 23 which is disposedwithin the metal shell 14 (or 13) and is packed tight withheat-resistent material 24 such as asbestos.

The cap 20, which is secured to the outside of the tubular portion 12 bya heat-resisting cement, comprises a cylindrical sleeve which is brazedto a washer 25 which in turn is brazed to the rod 23. An externalflexible current lead (not shown) is attached to a second washer 26.Current is conveyed to the electrode rod 16 by molybdenum foils 27embedded in the seal between the tubular metal shell 14 and the portion12 of the envelope. The leads from the foils are attached to the washer25. Therefore the current is carried from washer 24 through themolybdenum foils 27 by way of the metal shell 14 to the electrode 16.

This end cap construction provides a large area of engagement betweenthe metal supporting parts and the glass or silica parts and thusreduces the stress loading on the brittle silica under shock andvibration and reduces the risk of loosening of the caps.

The projections 19 are preferably omitted to allow some resilience inthe support of the anode and cathode. This is found to result in thetube being less susceptible to shock or vibration. It is also difficultto ensure that the projections 19 are a tight fit in the tubular portion1 l or 12 and if they are not the hammering of the projections againstthe tube will tend to weaken it.

We claim:

1. A high pressure xenon discharge lamp comprising an envelopecontaining a fill gas and having tubular end portions and a centralenlarged portion between said end portions, electrode structures of rodformation, and stems in each of which at least part of said electrodestructures is embedded, each stem having an outer end which is sealed bya metal shell and supported within one of the tubular end portions ofthe envelope and an inner end which is disposed within, but spaced fromthe said tubular end portion by a series of projections; a metal end caphaving an internal metal rod and a conical locating recess on its outersurface filled over the tubular end portions; and current conveyingmeans fitted between said electrode and said metal end cap.

2. A lamp according to claim 1 where said metal rod secured to said endcap extends within the said tubular shell, and a body of heat-resistingmaterial is packed between said metal rod and said tubular shell.

3. A lamp according to claim 1 where said current-carrying meanscomprises molybdenum foils sealed between said metal shell and thetubular metal end caps of the envelope.

1. A high pressure xenon discharge lamp comprising an envelopecontaining a fill gas aNd having tubular end portions and a centralenlarged portion between said end portions, electrode structures of rodformation, and stems in each of which at least part of said electrodestructures is embedded, each stem having an outer end which is sealed bya metal shell and supported within one of the tubular end portions ofthe envelope and an inner end which is disposed within, but spaced fromthe said tubular end portion by a series of projections; a metal end caphaving an internal metal rod and a conical locating recess on its outersurface filled over the tubular end portions; and current conveyingmeans fitted between said electrode and said metal end cap.
 2. A lampaccording to claim 1 where said metal rod secured to said end capextends within the said tubular shell, and a body of heat-resistingmaterial is packed between said metal rod and said tubular shell.
 3. Alamp according to claim 1 where said current-carrying means comprisesmolybdenum foils sealed between said metal shell and the tubular metalend caps of the envelope.